Microtektites and Associated Minerals in the Iridium-Rich Layer of Marine Clay From the Central North Pacific Ocean

Abstract:

Our study is based on a sample derived from a deep sea core (GPC3) from the mid-Pacific Ocean floor north of the Hawaiian Islands, provided by Jim Broda, Woods Hole Oceanographic Institution. The 65 Ma K/T boundary layer was identified by measurements of magnetic susceptibility (Doh, 1987) and Ir anomaly (Kyte et al., 1995) which peaked at a down-hole depth of 2055-2056 cm. Our sample of red clay was about 5 cubic cm in size. After wet-sieving for the size fraction greater than 38 microns, we hand-picked grains of interest under a binocular microscope. We found 40 microtektites (glass spherules, mostly devitrified), 12 olive-green aggregates composed of talc/magnetite, and 3 green and blue crystals of silicon carbide (SiC). There are many quartz grains having decorated deformation lamellae or mosaic structures.

The olive-green talc/magnetite particles have textures and composition similar to materials found in chondritic meteorites, whereas, SiC crystals are known to occur in carbonaceous chondrites. These particles seem to implicate an affinity to meteorites. Ir-rich deposits world-wide are believed to have settled from dust produced by the Chicxulub Impact, but what object from space created the impact crater is rather uncertain. Our results reported here cannot rule out the possiblilty of impact by comets, because the nature of cometary dust particles are not very well known.